Leonardo DiCaprio looks like he’s 12 years old. This is pretty astonishing, if you think of it. Eight years ago, in Titanic, he looked about 16. Now he seems to be sliding from a tenuous adolescence back toward a dewy, cherubic childhood. Is he really getting younger? Is this a case for Ripley’s Believe It or Not? Is there something in his chromosomes that can be bottled? Actually, what we’re witnessing may be an optical illusion caused by the role Leo plays in Martin Scorsese’s The Aviator: the legendary zillionaire Howard Hughes. If the actor (who turned 30 this year) had been playing the standard sort of 20-something he’s essayed in films like The Beach, perhaps he’d only look like a teenager. But playing Hughes, who not only had a lean and feral look but, moreover, left his most indelible impression as a bizarre septuagenarian recluse, Leo, in comparison, looks less than juvenile. He looks practically embryonic.

It’s no small irony, surely, that although DiCaprio is actually older now than Hughes was when The Aviator begins, we don’t experience him as a convincingly young Howard Hughes but as an actor who looks far too young to play Howard Hughes at any age. Yet once you process that, you realize that age may not be the crucial factor after all–nor may acting ability, since Leo remains a committed and capable performer. What’s really at issue is that he’s simply the wrong type for this role. He’s all blond and soft and delicate. Playing the dark, sinewy, rangy Hughes, he keeps coming off as Dennis the Menace trying out Dad’s shaving brush.

I’ll admit that I kept being snapped out of The Aviator‘s drama–the last thing the filmmakers want–by thoughts of how weirdly young and otherwise inappropriate the star seemed. After a while that gave way to thoughts like this: “Typical Hollywood. Scorsese spends a long time developing a project about Hughes, and then the money guys tell him he can only get it made if he casts Titanic‘s heartthrob in the lead. If Rin Tin Tin had the same box-office clout, no doubt he’d be flying those planes.”

But I had it wrong. Turns out DiCaprio was the one who developed the project, after reading a bio of Hughes years ago and becoming fixated on making a film about him. The star, who is also The Aviator‘s executive producer, obviously put a lot into the movie. And his central role (apart from the acting) casts its grandiose ambitions and equally outsized weaknesses in a decidedly different light.

Many people, after all, will read the film as a projected self-portrait by Scorsese. Since The Aviator spends a lot of its exorbitant three-hour length on Hughes as the obsessive, maniacally perfectionist maker of Hell’s Angels, Scarface and other Hollywood classics–it’s fascinating, to be sure, that the aviation tycoon’s career rhymed actual flying with flights of celluloid fantasy–you can see why the equivalence of auteur and protagonist would be assumed. Scorsese is legendarily the most movie-obsessed major American director ever, and here’s his first big movie literally about the movies, about an extravagantly determined filmmaker operating in the fantasyland of Golden Age Hollywood.

Yet I would submit that such a reading is essentially wrong, and that this is proved mainly by the way the movie feels. Certainly, you sense that Scorsese was invested in its craft and technique; these are his specialties, he has lots of state-of-the-art cinematic toys to play with this time out, and he does so with both expertise and exuberance. But, apart from a certain inevitable identification with Hughes in the moviemaking scenes, he doesn’t seem that invested in the character or his story. And there’s a simple reason for that: This is Leo’s show. Marty is the accomplice, the hired gun, the decorator of another man’s house.

So what has Leo wrought in his projected self-portrait? Well, the most salient feature of his Hughes is that he seems to have no inner life. He’s a guy who does all these amazing things–flying, making movies, loving various beautiful ladies, fighting the government, eventually going bonkers–yet we never get the slightest sense of what motivates him, how he decides to do anything, or how he feels about any of it.

Again, in a technical sense, Leo is not a bad actor at all. He performs with considerable confidence and authority, and looks about as convincing as he could, considering that he’s totally wrong for the part. Yet all that expertise is expended on the character’s exterior. He seems to have nothing at all inside. Is that, however, not a bizarrely apposite premise for a self-portrait by a huge young movie star whose sense of himself may well be that he is entirely constituted by how he is perceived by others? That he is literally all world-famous outside and no inside?

Perhaps so. But this takes us into the realm of unintended consequences, not art. Art presupposes a look inside the character, a sense of the meaning (both to him and to us) of his actions, an interpretation of his life. And these are precisely the dimensions The Aviator lacks. John Logan’s DiCaprio-commissioned script seems crafted to escort Hughes through an array of intense and colorful biographical situations, as if hurrying an actor across elaborate sets on a Hollywood soundstage; it never begins to ask who he was, why he did it all, or what it meant.

Perhaps the problem lies with “mythic” characters, especially ones considered mysterious. It strikes me that of the four notable biopics issuing from Hollywood this season, the two that offer the most engaging portraits deal with more or less human-scale men, the sexologist in Kinsey and the singer in Ray. It’s the movies that take on the big icons, Oliver Stone’s Alexander and now The Aviator, that leave us feeling like we’re gazing at figures as huge and hollow as Macy’s Christmas parade floats.

Yet the character Howard Hughes perhaps most resembles, the thinly fictionalized William Randolph Hearst of Citizen Kane, proves that not all such icons are undramatizable. To be sure, Welles’ publishing magnate is finally inexplicable (a grand symbol of any human personality’s ultimate mystery). But Kane also gives us a very elaborate, pointed and provocative interpretation of the man and his world, and beyond the enigmatic core it recognizes, it presents a complex and believable personality, complete with an expansive inner life that’s vividly mirrored in the expressionistic phantasmagoria of the film’s visual plan.

It’s precisely that correlation, the meaningful meshing of personality and style, which explains Kane‘s greatness and indicates The Aviator‘s central weakness. Granted, what Scorsese has done here stylistically recalls the giddy extravagance of Welles and other Golden Age studio wizards, and is purely fascinating on its own terms. If Scorsese’s our most erudite cinema professor, this film comprises an astonishing master class in movie technique (in that sense, it’s perfect for the age of DVD-as-tutorial-cum-museum-tour). Besides orchestrating rapturous contributions from cinematographer Robert Richardson and designer Dante Ferretti, the director provides a breathtakingly lush visual palette by evoking the “two-strip” and “three-strip” Technicolor techniques of the ’30s-’50s, and marrying these with some extremely adroit and innovative special effects, miniature work and digital manipulation of the image.

All of this could well win Scorsese his first Best Director Oscar, and why not: The Aviator‘s deft dazzlements represent nothing more or less than Hollywood’s idea of great direction. But consider the downside: Due to the human vacancy at its center, the film also ends up an exercise in style for style’s sake, expressionism with nothing to express beyond its own facility. Alas, Hollywood has never despised such skilled emptiness.

It remains to be noted that the film offers an assortment of fringe attractions that may please viewers who are not, as I was, crushingly bored by the whole enterprise. In covering Hughes’ life from the late ’20s to the late ’40s, the narrative surveys (if not elucidates) a rich slice of historical terrain where politics, showbiz and industry converge and collide. And its panoply of characters occasion some interesting performances. I was not convinced by Cate Blanchett’s turn as Katharine Hepburn; while Cate does a good job with her vocal mimicry of Kate, she is neither facially nor physically right for the role. Kate Beckinsale makes a more compelling turn as feisty Ava Gardner, while Alec Baldwin brings an aggressive edge to Hughes’ airline adversary Juan Trippe. Such lights as these might have made for a galvanizing constellation, had the superstar they’re circling not given birth to a black hole.